1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to digital subscriber line (DSL) based communication systems.
2. Description of Related Art
Communication systems are known to enable a plurality of communication devices to communicate among themselves and with communication devices in other communication systems. Such communication devices, which may be computers, modems, facsimile machines, printers, personal digital assistants, et cetera, communicate voice, text, and/or video data. Such communication systems support the communication of data in accordance with one or more communication standards. As is known, there are a large number of communication standards for the communication of data and such standards vary from country to country. For example, there are a variety of standards governing digital subscriber line (DSL) communications and such standards vary from country to country.
As is further known, for a communication device to communicate via a DSL based system, the communication device includes a DSL modem. Typically, the location of the communication device with its associated DSL modem is referred to as the customer premises. The DSL modem at the customer premises is typically coupled via a twisted pair to a DSL modem at a central office. FIG. 1 illustrates an example of a DSL modem at the customer premise (CPE) coupled to a DSL modem at the central office (CO). The coupling is achieved via a twisted pair, which supports one DSL channel, and is one of a plurality of twisted pairs in a cable binder, or bundle of wires. In this example, the frequency allocation of the DSL channel is illustrated in FIG. 2.
As shown in FIG. 2, the DSL channel includes 4 frequency bands (band 1 through band 4). Each band may be allocated for upstream transmission (i.e., from the CPE to the CO) or downstream transmission (i.e., from the CO to the CPE). For example, bands 1 and 3 may be used for upstream transmissions while bands 2 and 4 are used for downstream transmissions. The width (i.e., frequency) and height (i.e., power) of each band may vary and are typically defined by one or more standards. For example, various DSL standards prescribe a frequency, or spectral, plan that define the transmit frequencies (i.e., start frequency and width) and associated powers (i.e., height) for each band. This is done primarily to minimize near-end-cross-talk between twisted pairs within a cable binder by having each twisted pair within a cable binder using the same frequency plan.
To support the DSL channel illustrated in FIG. 2, the CO modem and CPE modem of FIG. 1 each include two transmitters and two receivers. In addition, each modem includes a hybrid, which performs a 2-wire to 4-wire conversion, a summer, and a splitting multiplexer and a reconstruction multiplexer. Accordingly, for the example given where bands 1 and 3 are used for upstream data communications, the 1st transmitter of the CPE modem transmits the data in band 1 and the 2nd transmitter of the CPE modem transmits the data associated with band 3. The transmitters in the CO modem transmit the data in band 2 and data in band 4, respectively. Correspondingly, the receivers in the CPE modem receive the data in band 2 and band 4, respectively. Similarly, the receivers in the CO modem receive the data in band 1 and band 3, respectively. Alternatively, bands 1 and 3 may be used for downstream transmissions and bands 2 and 4 may be used for upstream transmissions.
The splitting multiplexers in the CO modem and CPE modem split the incoming transmit data between the respective transmitters. Conversely, the reconstructing multiplexers, reconstruct the data received from the respective receivers into a serial data stream.
When data can be allocated into all 4 bands, the CPE modem and CO modem are capable of transceiving data at a relatively high bit rate (e.g., greater than 5 Mbps). Typically, the shorter the twisted pair, the less cable loss and the less cross-talk the twisted pair, or loop, exhibits. Conversely, the cable loss and cross-talk increase as the length of the loop increases. When the cable loss and cross-talk increase to significant levels, the upper frequency bands (e.g., band 3 and band 4), become unusable. Thus, CPE modems coupled to the central office via shorter loops typically have higher bit rates than CPE modems coupled to the central office via longer loops. This creates a discontinuity in quality of service since some users have a higher bit rate than others.
Therefore, a need exists for a method and apparatus for a configurable modem that achieves high bit rates in a DSL system regardless of the loop length.
The configurable multi-port modem of the present invention substantially meets these needs and others. An embodiment of a configurable multi-port modem includes a plurality of hybrids, a plurality of receivers, a plurality of transmitters, and a switching module. Each of the plurality of hybrids is operably coupled to provide 2 to 4 wire coupling for a corresponding one of a plurality of twisted pairs that are coupled to the configurable multi-port modem. For example, many homes and businesses have multiple lines, or twisted pairs, coming into their homes or offices. Accordingly, the configurable multi-port modem includes the plurality of hybrids to coupled to these multiple lines, or twisted pairs.
Each of the plurality of receivers is operably coupled to convert inbound DSL signals into inbound data. Each of the plurality of transmitters is operably coupled to convert outbound data into outbound DSL signals. The switching module is operable to couple at least one of the plurality of hybrids to at least one of the plurality of receivers and to at least one of the plurality of transmitters based on a configuration control signal. For example, when the loop is relatively short, a single twisted pair may be utilized to carry the DSL communication. In this instance, the plurality of receivers and plurality of transmitters would be coupled to a single hybrid, where each receiver and transmitter processing a different frequency band.
As the loop length increases and the usable frequency band decreases, additional lines, or twisted pairs may be used. As such, if two lines are being used, two hybrids are used and the plurality of receivers and transmitters, via the switching module, are configured to process one frequency band of one of the twisted pairs.
Another embodiment of a configurable multi-port modem includes a plurality of input/output modules, a plurality of transceivers, a plurality of hybrids, 1st switching module, and 2nd switching module. The 1st switching module is operable to couple at least one of the plurality of input/output modules to at least one of the plurality of transceivers based on a configuration control signal. The 2nd switching module is operable to couple at least one of the plurality of transceivers (i.e., transmitter/receiver) to at least one of the plurality of hybrids based on the configuration control signal.
In this embodiment, if the loop length is short and the high frequency bands are usable, the configurable multi-port modem may be configured to utilize the multiple twisted pairs to support multiple DSL communications. As the loop length increases, and the corresponding number of frequency bands per twisted pair decreases, the configurable multi-port modem can be configured to support a single DSL communication over the multiple twisted pairs using the same number of transceivers.
In any embodiment of a configurable multi-port modem in accordance with the present invention, more uniformed quality of service can be provided to customers regardless of loop length while maintaining adherence to frequency plans of various standards.